1. Field of the Invention
This invention relates to a low load seal used for sealing of fluid.
2. Description of the Related Art
As a seal attached to a dovetail groove 31 of a trapezoid cross sectional configuration among various conventional seals, an O ring 30, as shown in FIGS. 9A through 9C, is generally used.
A seal 35 (disclosed in Japanese Utility Model provisional publication No. 3-127866) as shown in FIGS. 10A and 10B is known.
In the present invention, as shown in FIGS. 9A through 9C, the diameter of the O ring 30 is larger than depth of the dovetail groove 31 on a member 32, and a part of the O ring 30 protrudes from an opening portion of the dovetail groove 31. As shown in FIG. 9A, the O ring 30 does not fall out of the dovetail groove 31 because the diameter of the O ring 30 is larger than width of the opening portion of the dovetail groove 31. As shown in FIG. 9A, 30a is a parting line (flash) in forming to which the member 32 and member 33 come relatively close, as shown in FIG. 9B. The O ring 30 is pressed by a facing surface 34 of the member 33 to be squeezed and given a predetermined squeeze amount (rate), and fluid is sealed inside and outside of the O ring as a border.
As shown in FIG. 10A, the seal 35 disclosed in Japanese Utility Model provisional publication No. 3-127866 is formed in a cross-sectional configuration composed of a large arc portion 36 attached to the dovetail groove 31, and a pair of extruding portions 37, formed as to branch and extrude from the large arc portion 36 to the opening portion side of the dovetail groove 31. A sucker portion 39 is formed with the pair of extruding portions 37 and the concave portion 38. As shown in FIG. 10B, the member 32 and the member 33 come close to each other to press the sucker portion 39 onto the facing surface 34, and the sucker portion 39 adheres to the facing surface 34 by absorption to seal the fluid.
In the O ring 30, described with reference to FIG. 9, a large compression load is required to give the predetermined squeeze amount (which amount is distributed equally between the member 32, the member 33, and the O ring 30), sealing ability is decreased for deformation of mating faces of the members 32 and 33 (or permanent deformation of the O ring 30), and life of equipment (a semiconductor apparatus, for example) is shortened thereby. Further, the O ring 30 is difficult to attach because the diameter of the O ring 30 is larger than the width of the opening portion of the dovetail groove 31. The O ring 30 may be twisted in attachment, the parting line 30a may become the sealing face (the parting line 30a may contact the facing surface 34 of the member 33), and sealing ability may be spoiled.
In case of a gate valve in which the member 32 is a gate and the member 33 is a valve seat, a large difference is generated in the compression amount of the O ring 30 for dimensional tolerance of each part. Because the valve is composed of many parts, load excessively changes, and the mechanism is overplanned to resist the load. Further, insufficient compression amount in an assembled state may cause leaks, problems of increasing compression permanent deformation and dust, and generation of cracks due to excessive load, which works on the O ring 30. In the event that, both sides of the gate valve are atmosphere and vacuum or vacuum and vacuum, the position of the gate is changed by flection of the mechanism caused by pressure difference, compression amount of the O ring 30 is changed, and it is difficult to obtain an appropriate sealed state.
In the seal 35, described with reference to FIG. 10, it is necessary to elastically deform the large arc portion 36 significantly; namely, to give large squeeze amount because the sucker portion 39 is strongly pressed to the facing surface 34 by the elasticity of the large arc portion 36, as in FIG. 10B. Therefore, there is a problem in that the life of the equipment is shortened by high compression loads. Thus, the seal 35 can be easily damaged due to the strong force of members 32 and 33, between which extruding portions 37 are sandwiched.
A seal 40 shown in FIG. 11 (disclosed in Japanese Patent Provisional Publication Number 10-311430), which is fitted into a groove 41, of which a cross-sectional configuration is a rectangle having a shallow concave portion 42 on a bottom wall face side of the groove 41, and a half-circular protruding portion 43 on an opening portion side of the groove 41. The seal 40, of which the width on the opening portion side is set to be larger than the width of the groove 41 in unattached state, is compressed into the groove 41 to be prevented from falling off. With regard to the seal 40, pressing deformation of the half-circular protruding portion 43 is released by the concave portion 42. When the half-circular protruding portion 43 is pressed by the facing surface 34 of the member 33, a relatively large compression load is required to give the predetermined squeeze amount (rate). This is because the rate of width dimension w1 of the half-circular protruding portion 43, when compared to the width dimension w of the groove 41, is large and the rate of the protruding dimension h1 of the half-circular protruding portion 43 from the opening portion to depth dimension of the groove 41 is small.
It is therefore an object of the present invention, solving the problems above, to provide a low load seal having excellent attachability to a dovetail groove, prevented from being twisted when attached into the dovetail groove, and extending life of the equipment by demonstration of good sealing ability with low load.